1. Field of the Invention
The invention relates to a slide valve substantially made of plastic material comprising a housing which is provided with connecting means for connecting said housing to a conduit for a flowing medium, which housing contains a slide which is capable of movement transversely to the direction of flow of said medium between a closed position, in which the flow can be shut off, and an open position, in which said flow can be released. It is noted that the above conduit is in particular a conduit, tube or pipe of plastic material.
2. Description of the Prior Art
It is generally known to use a plastic ball valve or a plastic butterfly valve, for example, for shutting off the flow of a medium in plastic piping. In a ball valve, a ball is clampingly provided between two seats, whereby the valve can be closed or opened by rotation so as to shut off or release the flow by means of said ball. Although the known ball valve has the advantage that the ball is not disposed in the flow in any manner in the open position, it is experienced to be a drawback not only that the valve consists of a relatively large number of parts, but especially that it is highly liable to fouling, in particular when used with viscous media. Another drawback is moreover the fact that the effective passage of a ball valve is smaller than the nominal diameter of the pipe of the system of pipes that is to be connected thereto. Another drawback of the known ball valve is finally the fact that automatic control thereof is rather complicated, since the rotation of the valve requires a substantial moment, which may result in the valve breaking loose. Furthermore, plastic butterfly valves, for example, are known for shutting of the through-flow. With this type of valve, a butterfly-like body is rotated in order to open or close the valve. The advantage of this is the fact that the valve is less sensitive to fouling, but it is experienced to be a drawback that a completely free flow is not possible, since the butterfly-like body extends parallel to the direction of flow in the open position. In addition, dirt accumulates against the butterfly-like body, in particular with viscous media, which interferes with the free flow.
It will be apparent that in practice the known valves in the form of ball valves or butterfly valves have appeared to be unsuitable for shutting off the flow of in particular viscous media in a network of pipes. Accordingly, the invention relates especially, but not exclusively, to the shutting off of the flow of viscous media by using a slide valve. The term viscous medium is understood to mean a thick, liquid medium or a liquid containing solid constituents. However, slide valves as such are generally known. With the known slide valve, the housing consists of various parts which are fitted together by means of bolt/nut and/or riveted connections. The connecting means of the known slide valves comprise xe2x80x9csocketsxe2x80x9d or xe2x80x9csleevesxe2x80x9d, which are in turn connected to the piping by means of a glued connection. The result of all this is that replacement or repair of the known slide valve involves the removal of the valve as a whole from the piping, which in practice often means that the slide valve must be sawed out of the piping at the location of the glued connections. Replacing a packing for the valve is done by loosening the relevant bolt/nut and/or rivetted connections of the slide valve housing. A consequent drawback of this is furthermore the fact that automatic control of the valve is generally impractical with the known slide valve.
Accordingly, it is an objective of the present invention to provide an inexpensive and efficiently operating slide valve substantially made of plastic material, in particular for shutting off the flow of viscous media in piping, which enables easy replacement, repair, cleaning and/or inspection of the slide valve as a whole or of parts thereof, which allows the use of all various media pressures (with the restrictions imposed thereon by the design, of course), and which exhibits a low sensitivity to fouling. In order to accomplish that objective, a valve of the kind referred to in the introduction is characterized in that the housing comprises a lower housing, in which the connecting means are present, and an upper housing for the slide, which is detachably connected therewith. Preferably, the lower and the upper housing are detachably interconnected by means of a bolt/nut connection, a screwed connection, a connection comprising plastic inserts, a clamped connection or a dovetail connection. Inspection, repair or replacement is very easy with the present slide valve, since the upper housing accommodating the slide can easily be removed in upward direction, whilst the lower housing will remain present in assembled condition in the pipework.
In one preferred embodiment of a valve according to the invention, the lower housing and the connecting means are made in one piece. More in particular, the entire housing, that is, the lower housing and the upper housing, is formed by means of an injection molding technique.
In another preferred embodiment of a valve according to the invention, the housing and/or the slide is (are) at least substantially made of non-reinforced plastic material. It is thereby preferred to use a non-reinforced plastic selected from the group consisting of PVC-U, PE, PP, ABS, PVC-C and PVDF. In another preferred embodiment, the housing and/or the slide is (are) made of a reinforced plastic material, for example glass fibre or a mineral-reinforced plastic. It is noted that the above material designations relate to the following (plastic) materials:
In another preferred embodiment of a valve according to the invention, the slide is at least substantially made of a metal, preferably stainless steel. The slide is preferably controlled by means of a manually, mechanically, electrically, pneumatically or hydraulically operated driving mechanism. The metal slide may be coated with a plastic or a rubber.
In another preferred embodiment of a valve according to the invention, the connecting means comprise a flanged connection, a threaded connection, a key/sleeve connection and/or a glued connection, whereby xe2x80x9csocketsxe2x80x9d or xe2x80x9csleevesxe2x80x9d present on the lower housing are accordingly fixed to piping. All this will be explained in more detail yet in the description of the figures.
Another preferred embodiment of a valve according to the invention comprises a seal provided in the lower housing, which seal is in particular detachably provided in a correspondingly shaped recess in the lower housing. Preferably, the seal can form a guide for the slide thereby. The seal thus incorporates three different functions: sealing the slide with respect to the flowing medium, sealing the lower housing and the upper housing from the outside, and, as already mentioned before, guiding the slide.
In another preferred embodiment of a valve according to the invention, the seal is at least substantially an envelope-like seal. The seal has in particular been formed by means of an injection moulding technique, using a rubber, preferably selected from the group consisting of NBR (nitrile butadiene rubber), EPDM (ethylene/polypropylene/diene/monomer) and F. P.M. (fluorocarbon elastomer), known under the brand name xe2x80x9cVitonxe2x80x9d.